Treatment of drilling fluids



Patented July 8, 1952 No Di'awing; Application- September 20.19.48,

Serial No. 50,017 7 lclaiin.

This invention relates generally to the treatment of mud-laden or drillin fluids, and parti'cul arly to the treatment of such fluids as are employed in the rotary drilling of oil and gas wells so as to improve the physical properties of said fluids. This application was copending with application Serial No. 277,564, filed June. 5, 1939, now Patent No. 2,452,021, issued October 19, 1948.

The fluid employed for rotary drilling operations and which is also called a drilling mud and a mud-laden fluid, may be made from the natural clay which occurs at the location or may be synthetically compounded from the clay and mud bases of commerce, including bentonite and beidellite. Such a fluid therefore contains a gelforming constituent which is generally'bentonitio in its nature. Such fluids may also contain a heavysubstance such as barytes, iron oxide, or the like, for increasing the specific gravity'of the fluid. Such a fluid is herein designated, descriptively, as an aqueous well drilling fluid.

Such fluids as are synthetically compounded may be controlled as to viscosity by a proper variation of the colloidal or gel-forming content, but when the cuttings from the bore hole become entrained in the fluid, its composition has changed, and further control is often necessary in order to maintain the desired viscosity but at the same time to permit the cuttings to settle out and render the fluid of such character that it will not be susceptible to gas cutting. With fluids which are compounded with the clay at the location, itis obviousthat such control is more difilcult. Furthermore, it is sometimes desirable to reduce the viscosity of drilling fluids initially.

The colloidal fractions of bentonite, as well as those of various clays obtained from widely difiere'nt locations, are quite similar in their composition With respect to silica, alumina, and iron, the main deviation only being from 10 to per cent of the average of each of these substances. The differences in properties exhibited by mudladen or drilling fluids prepared from clays and clayey materials obtained from various sources are largely due to varying proportions of calcium and/or magnesium present in the colloidal fraction and to thelarger proportion of non-colloidal inert'material contained in the same clayey suspension. in all cases these gel substances are complex hydrous silicates containing considerable proportions of aluminum and, in fact, may be classed either as hydrous alumino-silicates or in some instances hydrous silico-aluminates. Such substances invariably contain appreciable quantities of calcium and/or magnesium in their 2 composition and it: has been observed that; the corresponding sodium or potassium compound does not possess the same degree of gelatinous properties and the accompanying high viscosity that is associated with the corresponding alkaline-earth bearing hydrous silicates.

One of the objects of this invention therefore is to provide a process of controlling "the'characteristics of a mud-laden drilling fi'uid ofthe character described. i

Another object is to provide a'mud-laden drilling fluid of the character described which has improvedproperties; I

Further objects will appear from the following description" in which will be-setforthanomb'er ofembodiments of this invention-1 it will be understood that this invention is susceptible of various embodiments within the scope oi -th'e' ap pended claim.

Generally stated and in accordance with an illustrative embodiment of thisinvention, a drilling fluid of the character described treated with an alkali-metal arsenate, alone or with a lyophile colloid, to attain a drilling viscosity; of for example 15-60 centipoises Stormer; The arsenate, alone or with the lyophile colloid, is added to the drilling fluid during the course-of; drilling to maintain the same at such a viscosity.

The tests described in the following examples; were conducted on well drilling fluids prepared largely from Wyoming bentonites and water'so as to have a maximum content of thehydrous' aluminum silicates which are reacted upon-in the manner herein described. Drilling fluids prepared from natural clays and shalesusually encountered during drilling operations are similarly acted upon, since in all cases the colloidal fractions of such materials are quite similar in composition and properties to the purer colloidal gel-forming material, bentonit'e.

The arsenates preferably are derived from the pentoxide, AS205, in manner analogous to the preparation of phosphates from phosphorus pentoxide, P205; Pol'yarsenates may likewise"- be prepared as arsenate fusions or glasses-J Ekcampl 1 Tests were run with anhydrous disodium monohydrogen arsenate, as comparedwith tetrasodium pyroarsenate', prepared by fusion of disodium monohydrogen orthoarsenate,- using an-8 per cent Wyoming benton'ite fluid which had T. u ns-.1 1

3 by determination in a Stormer viscosimeter at 600 R. P. M.

Viscosity in Centipoiscs Example 2 The ortho-arsenates are more valuable as degeling agents when used with a lyophile colloid. As a specific example, several samples ofjthe same drilling fluid described under Example 1 were treated with disodium monohydrogen ar-y senate in the proportion of 0.40 g. per 100 ml. of drilling fluid together with varying proportions of dry chestnut tannin of 66% tannin content. The results are shown below.

The preceding examples exemplify the use of my improved degeling agents on a normal mudladen drilling fluid prepared in the usual manner from natural or synthetic mud-making materials. The relatively small proportions disclosed are normally suflicient to obtain a satisfactory treatment. However, if it is desired to add larger quantities of gel-forming materials such as bentonite, it is also necessary to use larger proportions-of the treating agent, usually from 0.5 to 2.5per cent, or even higher, based on the weight of the drilling fluid; The excess of treating agent reduces the gel-forming properties of the excess bentonite or 1 other material added, and thus allowslarger proportions of gel-forming material towater than normally can be incorporated in the drilling fluid. For instance, wherein a nor- ;mal-8-per cent suspension of bentonite in water may have a viscosity of 48 centipoises in the Stormer viscosimeter at 600 R. P. M., if the drilling fluid contains as much as 2 per cent of the treating agent, very much largerquantities of .bentonite may be incorporated without unduly increasing the viscosity. In fact, fluid muds may thusbe prepared from bentom'te which approximates the solids composition of muds-prepared ;from natural sources.

It is like wise obvious that muds which have become contaminated with cement, calcareous shales, and/or other sources of polyvalent metal compounds which have produced abnormal viscosities, will require heavier treatment with my improved treating agent to produce normal viscosities for muds so contaminated.

Where water is employed to thin or reduce the viscosity of a drilling fluid, large percentages of water as related to the drilling fluid are required vto effect such result. In the treatment ofpa drilling fluid with a chemical agent or compound,

however, comparatively small percentages are re- 4 quired to secure comparable results. It has also been known that adding a chemical to a drilling fluid would initially cause a thinning and then thickening by over-treatment. It was also known that the action of a given chemical on different drilling fluids are different; the practice of performing preliminary experiments or trials or preliminary try-outs, particularly in the laboratory, witha chemical on a drilling fluid, before a full scale try-out in a well was therefore resorted to. It was also known that the viscosity of a drilling fluid was increased by contamination by calcium compounds occurring in the drilling fluids or in the formations being drilled. It was therefore the practice to add a chemical in amounts, based not on a percentage as related 11 to the drilling fluid, but determined by the character of the drilling fluid and according to the nature of the strata being drilled. In the drilling of a well, the practice has been to take viscosity measurements and to add the chemical in amounts required to correct the viscosity.

The above tests as related to the various polyderivatives disclosed, are of course laboratory tests, made in order to show the comparative eiflcienci'es of the various agents enumeratedin the" treatment of drilling fluids. Inthe actual treatment of drilling fluids, the procedure is not one of using a given proportion or percentage of the treating agent with reference to the drilling fluid; the treatment is one of adjusting the viscosity of the drilling fluid by the addition of the treating agent. This will be apparent when we consider the fact that during the course of drilling a formation which may contain salts, cement, or cuttings, generally the viscosity will be affected by theaddition of these formation ingredients.

The water used in the making of the drillingv fluid, the temperature at the bottom of the well (which, in some wells,-may be above the boiling point of water), and other conditions also affect the viscosity of the drilling fluid. The practical procedure, therefore, is to add the treatingagent in accordance with the requirements in order to secure the desired'viscosity and thixotropicproperties and, in general, the desired reduction of the viscosity of a drilling fluid which has become contaminated by the ingredients of the formation.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is: 7

An aqueous welldrilling fluid of the character described and containing a gel-forming constituent, containing sufficient of a degelling alkalimetal ortho-arsenate and of a lyophile colloid to'attain a drilling viscosity.

TRUMAN B. WAYNE.

REFERENCES CITED UNITED STATES PATE TS 2,452,021 Wayne Oct. 19,1948 v OTHER REFERENCES Searle: The Chemistry and Physics of Clays and Other Ceramic Materials, 1924 ed., pp. 247-9.

Craft et al.: Effect of Arsenates on the Vis- .c'osity. of Drilling Muds, article in the Oil Weekly, October 15,1945, p. 66. 

